Frequently cited as the most corrupt mayor in American history, William Hale Thompson was elected to the mayor's office in Chicago in 1915. Losing his post in 1923 due to a bribery scandal, Thompson returned to power in 1927 with the promise of keeping open the businesses that had been shuttered by the previous administration, specifically speakeasies that had taken root in violation of Prohibition laws.
Thompson's campaign was field by criminal cash, including notorious gangster Al Capone, and Thompson even brought gang affiliates into city hall during his administration. Thompson only lasted one term before losing another reelection bid.
Since Thompson's departure from office, no other Republican has yet been elected mayor of Chicago.